1. Field of the Invention
One embodiment of the present invention relates to a phosphorescent organometallic iridium complex that is capable of converting triplet excited energy into luminescence. In addition, one embodiment of the present invention relates to a light-emitting element, a light-emitting device, an electronic device, and a lighting device each using the phosphorescent organometallic iridium complex.
2. Description of the Related Art
A light-emitting element having a structure in which a light-emitting layer including an organic compound that is a light-emitting substance is provided between a pair of electrodes has attracted attention as a next-generation flat panel display element in terms of characteristics such as being thin and light in weight, high speed response, and direct current low voltage driving. Further, a display device including this light-emitting element is superior in contrast, image quality, and has wide viewing angle.
Some of organic compounds which can be used for a light-emitting layer are capable of emitting phosphorescence from an excited state. Phosphorescence refers to luminescence generated by transition between different energies in multiplicity. In an ordinary organic compound, phosphorescence refers to luminescence generated in returning from the triplet excited state to the singlet ground state (in contrast, fluorescence refers to luminescence in returning from the singlet excited state to the singlet ground state). When such a compound capable of emitting phosphorescence, i.e., converting triplet excited energy into luminescence (hereinafter referred to as phosphorescent compound), is used as a light-emitting substance in a light-emitting layer, internal quantum efficiency can be increased to allow a light-emitting element to be highly efficient.
As a phosphorescent compound, an organometallic complex in which iridium or the like is a central metal has attracted attention and a variety of novel organometallic complexes have been synthesized (for example, see Patent Document 1), but control of a coordination position of a ligand with respect to a central metal is becoming necessary for efficient synthesis of an organometallic complex with a desired structure.